| Research Abstract |
General structures of the primary facial taste center (facial lobe) were histologically examined in various species of fish. The results show 6 types of the facial lobe (FL) organization: single column type, two lobule type, three lobule type, five lobule type, fusion type and maminar type. The single column type consists of the bilaterally symmetric column located adjacent to the fourth ventricle. The anterior, intermediate and posterior portions of the column receive projections mainly from the facial, glossopharyngeal and vagal nerves, respectively. The single column is considered to be the most primitive and may differentiate into fusion type, multiple lobule types or lamina typeswhich are found in cyprinid fish, catfish and goatfish, respectively.
In order to the somatotopic map, the central projections of various branches of the facial nerve were examined in three species of catfish, Parasilurus asotus, Plotosus lineatus, Arius felis by using technique of transganglionic tracing w
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ith horseradish peroxidase. The Parasilurus, Arius and Plotosus have two, three-four and five lobule type of the FL, respectively. Each lobule is a longitudinal subcolumn and become unclear in the posterior region of the FL. Tracing of nerve fibers shows that each lobule except the laterodorsal lobule receives input of a single barbel. For example, the four roughly equal, Longitudinal subcolumns of the Plotosus have input from four similarly-sized barbels, respectively and a fifth column represents the flank. On the other hand, the long, medium and short subcolumns of the Arius receive projections from the long maxillary, medium lateral mandibular and short medial mandibular barbels, respectively. These results clearly show that the multiple lobule types of the FL found in the catfishes is related to the number and length of the barbels, and that the somatotopic organization of the FL is essentially the same among the three species. The anterior-posterior axis of the barbels is represented in the FL in the same axis, while the anterior-posterior axis is represented in the FL in a posterior-anterior axis. Less
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